Rock bolters, independent of whether they are platform- or turret-type bolters, employ mechanisms to sequentially bring a drill and a bolt driver into alignment with a work axis which corresponds to the axis of the hole to be drilled and the bolt to be positioned therein. These mechanisms can be either a platform transfer device, such as taught in U.S. Pat. Nos. 5,114,279 and 5,690,449 or, alternatively, a turret transfer device such as is taught in U.S. Pat. Nos. 4,473,325 and 4,497,378. In either case, the drill is first aligned with the work axis and advanced to bore a hole into a desired location on a rock surface. The drill is withdrawn, and the bolt driver is then aligned with the work axis to advance the bolt into the hole. The bolt typically has a bolt plate associated therewith which is brought into contact with the rock surface when the bolt is fully inserted into the hole.
To assure that the bolt is accurately aligned with the axis of the drilled hole, a bolt centralizer, while not a necessity, is highly desirable. While a centralizer is desirable, the use of a centralizer does increase the complexity of the rock bolter. The centralizer should be, at least in part, positioned in close proximity to the hole and requires a bolt-directing element having a passage therethrough which needs to be in close proximity to the rock surface into which the hole is drilled. The introduction of a bolt centralizer presents two problems. The centralizer must not interfere with either the bolt driver or the bolt plate as the bolt driver is advanced, and the centralizer must have its bolt-directing element be retractable when the bolt is partially driven so that the bolt plate can be advanced to the rock surface.
The ""378 patent teaches a rock bolter which does not employ a centralizer, but instead relies on a pair of grippers for holding the bolt as it is transferred from a bolt magazine into alignment with the hole, these grippers apparently also serving to guide the bolt into the hole bored in the rock. The grippers are described as being pivotably mounted, and thus presumably pivot out of the way as the bolt driver and the bolt plate are advanced, allowing the bolt plate to be advanced into contact with the rock surface. Accurate alignment of the bolt with the hole has been found problematic with such devices, frequently requiring the operator to adjust the position of the rock bolter visually to insert the bolt into the hole. Even when bolts having a tapered bolt tip to assist in inserting the bolt into the hole are employed, accurate alignment of the bolt with the hole is problematic.
The ""325 patent, assigned to the same assignee as the ""378 patent, teaches the use of a centralizer in combination with the rock bolter described in the ""378 patent. The centralizer has a bolt-directing assembly with a bolt plate holder which positions the bold plate to allow the bolt plate to serve as the bolt-directing element. This approach requires the bolt plates to reside in close proximity to the rock surface, limiting the ability to store multiple bolts with the bolt plates residing thereon in a magazine when the rock bolter is intended for use in mines where the footprint of the front surface of the bolt magazine needs to be minimized to avoid interference with the surrounding rock surface during the bolt-setting operation. Also, since there are various configurations of bolt plates which are commonly used, a different holder would need to be used for different types. This would require alteration of the rock bolter when the plate type is changed, which is undesirable.
The ""279 patent, which is for a platform-type rock bolter, employs an arm to help transfer the bolt to the work axis and may also use the arm to direct the bolt into the hole. The arm has a hydraulic cylinder that causes it to grip the bolt and a second hydraulic cylinder that pivots the arm about an axis parallel to the work axis. The ""279 patent does not discuss how the arm is moved to allow the bolt plate to pass thereby. The use of two hydraulic cylinders to operate the arm complicates both the structure and the operation of the rock bolter.
Applicant""s assignee has overcome the problem of centralizing the bolt for most situations with the use of a combination stinger/centralizer, as taught in U.S. No. Pat. 5,556,235 and U.S. Pat. No. 6,413,019, for both of which the present Applicant is a co-inventor. The stinger/centralizer has two mating heads which form the centralizer, and which can be separated and withdrawn to allow the bolt plate to be advanced therepast. While the stinger/centralizer has been advantageously employed in many situations, the use of a stinger/centralizer may not be practical when clearances are severely limited, as the stinger/centralizer increases the overall height of the rock bolter. Additionally, when the rock surface is extremely friable, it is preferred to use the bolts to secure a screen material to the rock surface to stabilize it, and the presence of a stinger/centralizer may result in interference with the apparatus for handling such screen material.
Thus, there is a need for a centralizer structure for maintaining alignment of a bolt with respect to a pre-drilled hole which is suitable for use in limited clearance situations and for use with a screen handling apparatus.
The present invention is for a bolt centralizer that has utility in rock bolters which have frames and employ either platforms or turrets attached to the frames to move a rock drill and a bolt driver onto and off of a work axis. The work axis is defined as the axis which is traversed by a drill steel while being advanced by the rock drill to form a hole at a desired location on a rock surface and the axis along which a bolt is advanced when the bolt is being driven into the hole by the bolt driver. Further descriptions of these rock bolters are found in U.S. Pat. Nos. 5,556,235 and 5,690,449, and in U.S. patent application Ser. No. 09/691,736, all of which are assigned the assignee of the present application.
The bolt centralizer of the present invention has an arm terminating in an arm first end and an arm second end. The arm first end is connected to the frame of the rock bolter. A bolt-directing hand having a hand first end and a hand second end is provided. The bolt directing-hand is pivotably attached to the arm second end so as to pivot about a hand pivot axis. This hand pivot axis is preferably normal to the work axis to allow the hand to pivot in an arc which is coplanar with the work axis.
A pair of fingers is pivotably attached to the hand second end such that the fingers pivot with respect to each other about a finger pivot axis between a closed position, where they are in a bolt-gripping relationship with respect to each other, and an open position, where they are in a bolt-releasing relationship. A spring is provided to bias the pair of fingers to the closed position. Preferably, the fingers are both pivotably mounted to the hand second end and share a common finger pivot axis that is positioned so as to swing through a plane which contains the work axis when the bolt-directing hand is pivoted about the hand pivot axis.
A recess is provided in each of the fingers and these recesses are configured and positioned such that, in combination, they form a centralizer passage when the fingers are in the closed position. The centralizer passage is sized to slidably engage the bolt when the bolt is positioned in the recesses and the fingers are in the closed position. Alternatively, when the fingers are in the open position, they are sufficiently separated as to allow the bolt to be passed into and out of the recesses.
Means for rotating the bolt-directing hand about the hand pivot axis are provided, and serve to rotate the bolt-directing hand between a first hand position, where the centralizer passage is alignable with the work axis, and a second hand position, where the hand and fingers are positioned so as not to obstruct the advancement of the bolt driver, a bolt plate mounted on the bolt, the rock drill, or a resin injector if one is employed. In the first hand position, the centralizer passage can be either in alignment with the work axis, when the bolt and the bolt driver are aligned therewith, or aligned only with the bolt and bolt driver when the bolt and the bolt driver are subsequently moved into alignment with the work axis. Preferably, the bolt-directing hand pivots such that the fingers are moved into closer proximity to the rock surface when the bolt-directing hand is moved from the first hand position to the second hand position. The means for rotating the hand are activated to move the hand from its second hand position to its first hand position to bring the fingers into engagement with the bolt or, alternatively, to bring the fingers to a position where the bolt engages the fingers as the bolt is advanced. The engagement of the fingers with the bolt serves to guide the bolt to facilitate implanting a bolt tip of the bolt into the hole which has previously been drilled along the work axis, since the centralizer passage is aligned with the work axis when the hand in the first hand position. After the bolt has been partially inserted into the hole, the means for rotating the hand are activated to move the hand to its second hand position, forcing the fingers to release the bolt and moving the hand and fingers off the work axis to allow the bolt driver to further advance the bolt to bring the bolt plate into contact with the rock surface.
Means for locking the bolt-directing hand in the first hand position are provided to assure that the alignment of the centralizer passage remains true as the bolt is being directed into and through the centralizer passage of the bolt centralizer. Preferably, the means for locking the bolt-directing hand in the first hand position are incorporated into the means for rotating the bolt-directing hand.
To further facilitate the engagement of the bolt with the bolt centralizer, it is preferred that the centralizer passage terminate in a beveled surface positioned to guide the bolt into the centralizer passage as the bolt approaches the fingers. The bolt can approach the fingers either as the bolt-directing hand is pivoted toward its first position or, when the bolt-directing hand is separated from the bolt when in its first position, as the bolt is advanced by the bolt driver. It is further preferred that the centralizer passage terminate in a beveled surface at its other end to reduce the torsional load required to open the fingers to release the bolt. If the bevels are the same, this brings an additional advantage in that symmetrical fingers can be used to reduce the number of parts that need to be maintained in inventory for repair.
It is also preferred for the fingers to each have a finger terminating region through which the bolt passes as the fingers are either swung onto or off of the bolt. These finger terminating regions each have a sloped surface adjacent the centralizer passage and secondary bevels which intersect the sloped surface. The sloped surfaces slope toward the centralizer passage and serve as ramp surfaces to force the fingers to their open position when the hand is pivoted from its first hand position to its second hand position to disengage the fingers from the bolt. The sloped surfaces can also assist in guiding the bolt into the centralizer passage when the bolt tip is misaligned with the work axis and the hand is pivoted into engagement with the bolt as it pivots from its second hand position to its first hand position. The secondary bevels may also assist in removing the fingers from the bolt, but primarily serve to force the fingers open in situations where the bolt tip is misaligned and the fingers are swung over the tip of the bolt as the hand is pivoted from its second hand position to its first hand position. Forcing the fingers toward their open position allows the bolt tip to engage the sloped surfaces and be guided into the centralizer passage. Alternatively, when shorter bolts are employed and the bolt tip is substantially aligned with the work axis, the recesses may be brought over the end of the bolt without requiring the fingers to be forced open, or the fingers may be brought to a position where they are interposed between the end of the bolt and the hole such that the bolt is brought into engagement with the fingers as it is advanced. Again, it is preferred for the fingers to be symmetrical.
While various actuators or mechanisms could be employed to provide means for rotating the bolt-directing hand between the first hand position and the second hand position, it has been found convenient to employ a linear actuator having an actuator first end and an actuator second end to provide the means. The linear actuator has the actuator first end pivotably connected to the hand while the actuator second end is pivotably connected to a structural element of the rock bolter which remains in a fixed relationship with respect to the arm. The use of a linear actuator has a second benefit when the actuator provides a firm maximum extension, in which case the actuator can also serve as the means for locking the hand in the first hand position.